1. Technical Field of the Invention
The present invention relates to a quadrature detection method and a related quadrature detection device for use in demodulating a modulation wave from a carrier wave subjected to amplitude modulation or phase modulation and a radio wave timepiece for extracting time information from a standard broadcast using such a quadrature detection device.
2. Description of the Related Art
In the related art, attempts have heretofore been made to provide a radio wave timepiece with a structure wherein a long wave standard radio wave subjected to amplitude modulation with time information, is received to allow time information to be demodulated from a reception signal to correct an own clock time.
With such a radio wave timepiece, it has been a normal practice to increase the reception sensitivity on the long wave standard radio wave through the use of a narrow-band-pass filter (quartz-crystal filter), utilizing a crystal oscillator, for passing the reception signal of which only a signal component, corresponding to a frequency of the long wave standard radio wave, is extracted to allow the reception signal, as a result of extraction, to be detected for thereby demodulating time information as disclosed in Japanese Patent Application Laid-Open Publication No. 2003-60520.
However, the quartz-crystal filter is hard to be formed in an integrated structure with the resultant difficulty of forming the related art radio wave timepiece in a miniaturized configuration. Especially, in countries or territories where a plurality of transmission stations transmit long wave standard radio waves at different frequencies (of two kinds including 40 kHz and 60 kHz in Japan) in an area like Japan, the radio wave timepiece usually needs a plurality of quartz-crystal oscillators so as to enable the use of both the frequencies and, therefore, undergoes a difficulty of obtaining the miniaturization in structure. Moreover, due to high costs of the quartz-crystal oscillators, another issue arises in an increase in manufacturing costs of the radio wave timepiece.
In the meanwhile, recently, another attempt has been made to provider a receiver unit that has a capability of demodulating time information from a long wave standard radio wave without the use of quartz-crystal oscillators upon which the reception signal is subjected to quadrature detection as disclosed in Japanese Patent Application Laid-Open Publication No. 2004-104555.
With such a receiver unit mentioned above, the operations are executed to perform quadrature detection of reception signal to demodulate time information in a sequence wherein the reception signal is divided into two distributions to cause the resulting reception signals to be mixed with a sin wave and a cosine wave at the same frequency as that of the long wave standard radio wave upon which an in-phase component I and a quadrature component Q of the long wave standard radio wave are extracted and these signal components I and Q are squared to be added. Although such a sequence needs for a standard signal (a signal at the same frequency as that of the long wave standard radio wave) to be generated for quadrature detection, no need arises for employing the narrow-band quartz-crystal oscillator as required in the related art practice and time information can be demodulated from the long wave standard radio wave.
However, due to the particular structure of the receiver unit proposed in the related art utilizing commonly used quadrature detection technique wherein the reception signals are mixed with the sin wave and the cosine wave, respectively, upon which the in-phase component I and the quadrature component Q of the long wave standard radio wave are extracted, a mixer in a trailing stage for mixing various signals needs to have a filter. Moreover, a distribution circuit has a preceding stage that needs to have an amplifier circuit with an AGC (Automatic Gain Control Circuit).
All of these component parts are made of analogue circuit elements that need to have a large number of outside parts such as resistors and capacitors or the like, resulting in deterioration in demodulating performance on time information due to variations in characteristics and temperature characteristics of these component parts.
Further, in general practice, the radio wave timepiece is comprised of a timekeeping and correction circuit, for keeping current time and correcting the current time based on time information, which is formed of a digital circuit. Therefore, the receiver unit of the related art is extremely difficult to be structured with the digital circuit and one chip with the resultant formation of the radio wave timepiece in a two-chip structure.
Accordingly, even if the radio wave timepiece takes the form of a structure employing the receiver unit mentioned above, issues arise with the occurrence of difficulties of forming the radio wave timepiece in a miniaturized construction and preventing deterioration in characteristics of the receiver unit resulting from temperature variations.